Objective: Bispectral index (BIS) is mainly used for drug titration and is well correlated with drug concentration and hypnosis. Our aim was to present the correlation between hypothermia and BIS during abdominal surgery. Methods: The study was conducted in patients with American Society of Anesthesiologists (ASA) score I-III, aged between 18-60 y, who had undergone abdominal operation in general surgery theatre. Body temperature and BIS scores when awake, after anesthesia induction, after tracheal intubation and every 5 minutes during the operation, and after extubation were measured and recorded. Results: Three hundred patients were included to the study. Repeated measure regression analysis of BIS scores with the body temperature at distinct time points did not show a significant relationship. None of the patients had a body temperature lower than 35°C. Conclusions: As a result of our study, we can say that temperature decrease up to 35°C may not have an effect on BIS scores, and BIS maybe used safely to indicate hypnosis level at temperatures 35°C and above during abdominal surgery.